The present invention relates to a bundle and a method for producing this bundle for which a plurality of printed sheets are gathered to form a book block and a plurality of book blocks, oriented in the same way and respectively positioned standing upright on the lower edges of the printed sheets, are then combined to form a bundle and are compressed. For this, two adjacent book blocks are positioned offset, relative to each other, prior to the compressing operation and are then fixed in position following the compressing operation. Bundles of this type are produced for intermediate storage of printed sheets with the aid of so-called bundle delivery machines. In the process, printed sheets which are positioned upright and lined up in a row are gathered to form a bundle, are subsequently compressed and then strapped together.
As is known, for the production of perfect-bound printed products such as hardcover books, paperback books and similar products, the required number of printed sheets and the covers are normally printed in an optional sequence during a first step and are then stored temporarily. For this, the printed sheets which can be folded individual sheets or signatures with glued-on fly leaf are gathered in the correct sequence to form loose book blocks, are combined with additional book components such as cases for hardcover products, fly leaves, combination fly leaves, or covers and are then supplied to a perfect binder where they are bound along the spine and are glued together with the cover or the slip-fold strip. By separating the printing process from the binding process, both processes can be realized with the optimum speed. However, it has turned out to be a disadvantage that the binding process can be carried out only after all printed sheets and covers have been printed, which requires a relatively large stock of printed sheets and covers.
Printing presses are also known which sequentially print all pages of a book and subsequently deliver complete, loose book blocks that can be supplied directly to a perfect binder. A printing press of this type is known from the U.S. Pat. No. 3,518,940. With this method, which is used rarely in practical operations, the intermediate storage of printed sheets can be avoided but it also requires an extremely involved printing press. In addition, this method only makes economic sense when it is used for extremely large editions and the achievable print quality is furthermore low.
Digital printing presses have been known for some time which sequentially print all pages of a book and then supply complete, loose book blocks that can be bound without requiring further operations. Accordingly, a digital printing press can be used to optionally produce one after another complete book blocks with differing contents. A further advantage of the digital printing press is that no printing plates are required. In addition to avoiding the costs of producing the printing plates, the operational interruptions necessary for replacing the printing plates are also omitted. The printed sheets or individual pages that form a book block are delivered in the form of a stack, for example deposited offset to each other on a pallet, such that they can be separated again easily later on. Alternatively, full-surface layers of book blocks can also be formed, wherein the layers are separated by an intermediate layer. Book blocks stacked in this way can be stored for an optional length of time before being supplied to a perfect binder.
The depositing of loose stacks on pallets can be effected manually or automatically with a so-called palletizer. A device of this type is disclosed in the European Patent document EP 2098465 A1. The loose sheet stacks of horizontally positioned printed products are removed again manually from the pallet at a later date and are supplied to the feeding region of a perfect binder. However, this solution has the known disadvantage that the loose book blocks are not sufficiently compressed along the fold region, thereby resulting in products which are considerably thicker in the fold region than in the flat region. In addition, the lower book blocks are compressed most and the top ones are not compressed at all. Poorly compressed book blocks or book blocks compressed with different strength can lead to serious problems during further processing or can hinder further processing.
European Patent document EP 2159070 A1, discloses that printed sheets in a stack are glued together along one edge region. As a result, the stacks can be separated again clearly at a later point in time, prior to the further processing. With this method, the printed sheets are also compressed irregularly or insufficiently, which results in the aforementioned disadvantages. The glued together printed sheets furthermore can no longer be aligned in the perfect binder. The surface area of the printed sheets, which is necessary for the gluing and must be cut off in the three-blade cutter during the final trimming step, represents a further disadvantage by considerably increasing the amount of paper used. An additional disadvantage results from the thickening of the stack at those locations where adhesive is applied to the printed sheets, thereby making the further processing more difficult.
Also known is a method of gluing the printed sheets together along the fronts rather than between the flat sides. In addition to the above-mentioned disadvantages of such gluing operations, this method has the further disadvantage that glue can be deposited on the paper guides during the further processing, thereby causing machine malfunctions and requiring cleaning expenditure.
Instead of depositing the stacks of printed sheets on pallets or similar devices, methods are also known for which the printing press is arranged and operated in line with the perfect binder. Since the printing press can print continuously, as previously mentioned, a buffer or storage section must be provided between the printing press and the further processing locations, wherein the buffer capacity must be sufficient to individually store the book blocks which are printed during a period of changeover to the further processing operations. Additional buffer capacity should also be provided in case the further processing operations stop for any reason. Alternatively, the book blocks printed during such an interval can also be transferred out and can be supplied once more later on.
European Patent document EP 1950159 A1 discloses a stack-type arrangement of flat printed products, wherein all printed products within the stack have the same orientation. One of the four sides of the printed products is thicker than the other sides, for example because the printed products have a fold or even a staple on this side. To ensure that these stacks have the same stability as the stacks composed of partial stacks which are offset relative to each other by 180°, the partial stacks in this case are offset transverse to the thicker side and alternating. In the process, the partial stacks are offset perpendicular to the lower edges in the direction of the stack height. Stacks configured in this way have the disadvantage that the printed products within the stack are compressed differently strong in the region of the thicker side, thereby causing the non-compressed fold regions to have a tendency to fan out.